I'm looking to book a JAL Premium Economy ticket, paying cash, but then transferring some miles into my JMB account to upgrade it to business. Are these awards instantaneous? Is there any way to search it? 30,000/each way to USA is a bit steep, but might be the price of comfort.

Most important, I need to then switch my frequent flyer number back to AA... can I do this after the upgrade is processed and before flying? Their website was clunky last I remember booking through them (it's been years), so I'm guessing I'd have to call it in IF I can switch it. I do need this credited to AA to hit OneWorld Emerald again.

Thanks